Ice Storage – How and Why….

TOOLS AND TECHNOLOGY
Ice Storage –
How and Why….
SAMPLE FLOW DIAGRAM WITH TRANE
CHILLERS AND CALMAC ICE STORAGE TANKS
Illustration: Trane
Eugene Garcia, ECM and
Todd Coulard, Trane
Ice storage installations are on the rise in the New York Metro
area. Large financially-driven institutions in the New York City,
Long Island and Westchester County areas are leading the way.
Attractive economics, environmental benefits, and added facility
reliability are turning thermal storage into a compelling design
option. Although there are other kinds of storage systems, such
as chilled water, ice storage technology makes the most sense
because of the typical space limitations in commercial buildings.
Richard Haley of the Trane Company, notes “the integrated design
of chillers and ice storage has a tremendous amount of benefit
for overall system flexibility. Customers are catching on to the
concept and it’s evident in the projects which we are executing.
In the last couple years, we have installed half a dozen major ice
storage systems.”
An ice storage system uses a chiller to make ice during off-peak
night time hours when energy is cheaper and then melts the ice
for peak period cooling needs, effectively shifting the electric load
and avoiding higher price energy and demand charges during the
day. The operation of an ice storage system is comprised of two
normal modes: the ice charging mode and ice melt/burn mode.
During the ice charging mode, there is typically a designated
ice-making chiller that is run for the purpose of producing low
temperature glycol to freeze the water inside an ice storage tank.
The glycol loop, consisting of the ice storage tanks, heat exchangers and pumps are isolated from the main building chilled water
loop (see flow diagram above). The ice charging mode continues
Thermal Energy Storage Tanks
Notes:
CWS = Condenser Water Supply
CWR = Condenser Water Return
SCHWS = Secondary Chilled Water Supply
SCHWR = Secondary Chilled Water Return
until the ice is fully frozen, usually about 8 to 10 hours and is done
during the utility’s off-peak period. Ice melt commences as the
building load increases and the temperature differential between
the chilled water supply and the chilled water return increases.
Economics
The economic benefits of ice storage are largely derived from
shifting expensive on-peak electric demand/consumption to the
cheaper off-peak electric rates. Avoided demand charges in Long
Island Power Authority (LIPA) and ConEd territories range from
$20 to $35/kW in the summer months and the spread between
on-peak and off-peak energy is usually 2.5 to 3 cents.
THE COSTS AND BENEFITS OF HIGH PERFORMANCE BUILDINGS
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TOOLS AND TECHNOLOGY
Additional savings are delivered from extended free cooling
periods and the efficient delivery of low flow/low temp systems
that reduce pump and fan power demand and consumption. Typical building operation dictates that free cooling benefits typically
can be secured up to an outdoor temperature of 50 degrees
Fahrenheit. Beyond that point, the transition back between free
cooling and mechanical cooling is risky. The potential for having
an entire chiller plant shut-down during normal business hours is
unacceptable. Ice storage acts as a buffer in that scenario, allowing
operators to become more comfortable with the operation of
free cooling during questionable outdoor air temperature levels.
Buildings can expect to add up to half of a month of free cooling
on either end of the summer.
With low flow/low temp, the benefits of delivering lower temperature chilled water to reduce the demand and consumption of
pumps and fans are well documented. However, using ice storage
to produce low temperature chilled water and avoiding chiller
efficiency penalties is not. Delivering 40°F chilled water, as opposed to 44°F can add another 0.1kW/ton of electric demand to
a chiller. Using ice to drive down the temperature eliminates that
chiller efficiency penalty. Over the past few years, simple paybacks
for ice storage installations in the New York metro area have
ranged from 3 to 5 years.
According to Walter Smith, Senior Vice President for Reckson
Associates Realty Corp that has put several ice storage facilities in
its buildings, “Reckson’s goal is to own one of the highest quality office portfolios in the tri-state area. Creating that portfolio
is dependent on putting in high quality infrastructure that meets
the financial needs of both our tenants and shareholders. Strong
financial management is integral to our success.”
Environment
The most basic function of ice storage is to shift on-peak electric
load to off-peak. Realizing that on-peak generation in the New
York Independent System Operator’s (“NYISO”) territory is considerably “dirtier” than off-peak generation, there are considerable
environmental benefits derived from the reduction of air polluting
emissions (NOx, SOx, and CO2). A typical central plant renovation, incorporating ice storage, provides environmental benefits
equivalent to planting hundreds of thousands of acres of trees or
removing a couple hundred cars from the road.
Ice storage delivers more than one type of “green” benefit. William
Beck, Managing Director of Global Engineering and Critical Systems
for Credit Suisse, said, “Credit Suisse is a financial institution that is
committed to the environment. Ice storage made perfect sense for
us. It’s good for business and good for the environment.”
Sites with data center or trading floor operations, typically strive
to reach a certain N+ level of reliability, or in some cases 2N. At
one of Morgan Stanley’s mission critical facilities, they are approaching a 2N level of reliability on their HVAC operations via
the utilization of ice storage. Daniel Pugliese, Operations Manager,
for Hines who manages the Morgan Stanley building has stated
“one of our performance based goals is to operate 24-7, 365
days a year. Ice storage combined with the piping configuration
that our team developed, not only helps us to meet those goals,
but allows us to exceed those goals by providing an added level of
reliability in an economically attractive fashion.”
Most mission critical facilities provide their massive cooling
needs with Computer Room Air Conditioning (“CRAC”) units.
These units typically incorporate a free cooling mode where the
compressors shut-down and the cool medium in the coils provide
the air conditioning needs. The units operate in the same manner
whether they are fed from a dry cooler system or a second feed
that comes from the central plant/ice storage loop.
Ice storage is providing less expensive cooling, more reliability and
decreased impact on the environment. Smart financial managers
are driving the marketplace towards ice.
Eugene Garcia is president of ECM Energy Management Services.
Mr. Garcia possesses more than 15 years of energy, engineering and
finance related experience. He has provided operational and strategic
planning to meet the needs of internal business requirements as well
as those of external customers. His technical experience includes the
design, procurement, and production of energy and its related systems.
His market knowledge is derived from both domestic and international
experiences related to the deregulation and privatization trends surrounding the energy industry.
Todd Coulard, manager of the Energy Services Group (“ESG”) of Trane
New York/New Jersey, has over 15 years experience in the design and
implementation of energy efficiency projects. He is currently responsible for the development and construction of large-scale comprehensive
energy efficiency projects for Trane. His group is involved in the project
estimating, budgeting, savings calculations, and providing hands-on
supervision and technical support to subcontractors. ESG assesses
client properties and evaluates site specific energy efficiency and capital
improvement measures, with an emphasis on economic viability for
clients. Mr. Coulard’s group develops Energy Performance program
proposals including financial analysis, financing options and statistical
analysis of client energy consumption profiles. Prior to joining Trane, Mr.
Coulard was Director of Facilities for the Durst Organization. He was
involved in the commissioning of Four Times Square, the development
of the 1155 Thermal Storage Project and implementation of energy
efficiency measures throughout the Durst portfolio.
Reliability
Batteries are to electricity as ice storage is to chilled water.
Similar to the way batteries act as a back-up for electricity, ice
acts as a back-up for chilled water. Ice storage can reduce the risk
of the transition between free cooling and mechanical cooling and
carry you through a temporary chiller shut-down, whether it is
during a free cooling operation or other operational quirk which
temporarily shuts down central plant chillers.
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THE COSTS AND BENEFITS OF HIGH PERFORMANCE BUILDINGS